Research On Microstructure And Corrosion Behavior Of Ti-Ta Alloys

The nuclear power industry of China have been rapidly developed in recent years. In order to improve the fuel efficiency and reduce the uncertainty risks of permanent storage, the nuclear fuel reprocessing research have paid more and more attention. Due to the nuclear fuel reprocessing facilities must be in the high concentration of nitric acid environments for a long time, the service environment is bad. Therefore, the development of the key equipment timber have a widespread concern in material workers.Ti-Ta based corrosion resistant alloys is widely used in nuclear spent fuel processing field because of its ability that have good resistance to oxidation in acidic medium and not sensitive to radiation. To avoid Ti-Ta alloys uneven corrosion by different processing status causing damage to the equipment of post-nuclear spent fuel reprocessing critical equipment components. It`s necessary to research on the corrosion rate and corrosion behavior of different processing status and organizational structure of Ti-Ta alloy in the boiling nitric acid.Different content Ta of Ti-Ta alloy and different processing states are selected to corrosion in 8mol/L boiling nitric acid to study the characteristics of the corrosion behavior. The differences of the corrosion behavior and the corrosion surface oxide film of Ti35 alloy and Ti-32 Ta alloy have been studied in the paper. The corrosion rate and electrochemical properties of different organizational structures of Ti35 alloy also has been studied. The main contents and conclusions are as follows:(1) The corrosion tests showed that Ti-32 Ta alloy have an order of magnitude lower corrosion rate than Ti35 alloy in the 8mol/L boiling nitric, the oxide film becomes thinner but more corrosion because of add a lot of Ta element; it`s little effect on the size of the residual stress caused by different processing methods of Ti35 alloy. It can significantly reduce the corrosion rate when the Ti35 alloy`s grain size increased. Ti35 alloy have a lower corrosion rate when it is welded.(2) The transition of surface color on Ti35 alloy is mainly caused by the different ion species at each stages of the oxide film. Nano-level oxide film is formed on the surface of Ti-32 Ta alloy after corrosion, the oxide film is more dense than Ti35 alloy`s. The oxide film is mainly composed by TiO2, TiO, Ti2 O, Ta2O5 and Ta elemental, the composition is the same as Ti35 alloy. Each component in the proportion of its elements are substantially equal, The main reason of Ti-32 Ta alloy`s oxide film have higher corrosion resistant level is the increasing of Ta content in the oxide film.(3) The electrochemical properties of titanium alloys can be improved by adding Ta element. The corrosion current density of Ti35 alloy is decreased and the charge transfer resistance is increased after adding 6% Ta element. The corrosion potential of Ti-32 Ta alloy is increased, the corrosion current density is decreased and the charge transfer resetance is increased after adding 32% Ta element.(4) The oxide film of Ti35 alloy has better corrosion resistance than the matrix. It has a lower surface corrosion potential than Ti35 alloy substrate, the corrosion current density is also lower than the matrix, the charge transfer resistance doubled. It has a intact, dense, defect-free surface oxide film, the corrosion process are uniform corrosion, no pitting. The etching rate of the oxide film is smaller than the substrate.(5) It has a better electrochemical performance that the Ti35 alloy bar after annealing, the corrosion current density is decreased, the pitting potential is rised, the charge transfer resistance is increased. Ti35 alloy sheet after welding has a better electrochemical performance than the matrix, the corrosion current density is decreased, the charge transfer resistance is increased.